1. Field of the Invention
In coordinate measuring devices, and in particular those of the so-called column type, relatively large vibrations occur in the machine structure in the course of acceleration and braking processes, and are not detected by the path measurement system, that is, with the scales of the coordinate measuring device, and hence lead to erroneous measurements. In the course of these vibrations the probe head of the coordinate measuring device is deflected from the null position given by the scales, and the position of the probe head at the moment of sensing, that is, when the probe element of the probe head contacts the workpiece, is thus not precisely defined. In column measuring devices, these vibrations occur with a large amplitude, particularly when the horizontal measuring arm or measuring beam of the device has extended fully and has traveled to the upper end of the vertical column of the device, i.e., into edge positions of the measuring region, where the machine configuration is less rigid.
2. Relevant Prior Art
It has indeed already been proposed, in U.S. Pat. No. 4,333,238, for coordinate measuring devices of the so-called portal type to detect the dynamic bending of the measuring spindle, which is vertical, of the device by means of an acceleration sensor and to correct the coordinate measurement value provided by the probe head of the device. Correction values for different places in the measurement region of the machine are selected, corresponding to the measurement values of the acceleration sensor, by means of an allocation rule which is not more closely designated.
The described system however has not heretofore been used for the correction of measurement errors due to vibrations in coordinate measuring devices, primarily because there is no simple allocation rule which can be found by calibration and with which the measurement values of the acceleration sensors can be recalculated into the associated deflection of the sensing element at the instant of the measurement. Accordingly, acceleration sensors are nowadays only used in coordinate measuring devices in order to sense the amplitude of the vibrations and to evaluate the corresponding signal for a monitoring of the obtained measured coordinate values in the sense of a Yes/No statement, "measurement valid" or "vibration amplitude too high, i.e. , measurement invalid", as for example is mentioned in DE-OS [German Laid-Open Patent Application] 4,035,923 and in the above cited U.S. Pat. No. 4,333,238.
It is known from U.S. Pat. No. 4,782,598 to permanently sense the inclination errors of the machine parts of a coordinate measuring device and, based on the known geometrical relationships between the machine parts, to calculate back to the position of the probe element. However, this process requires relatively many sensors at different places of the machine and supplies usable results only in static operation. Also here, the vibration of the machine parts is only evaluated, by means of a so-called "Vibration Filter (66)" (see U.S. Pat. No. 4,782,589, FIG. 9), in order to monitor the validity of measurement values in the sense of a Yes/No Statement.